Three-GPU Litecoin mining -- performance numbers don't make any sense

[eltopo71]

I got a Litecoin mining rig going yesterday using the excellent tutorial over at litecoin.info. So far things are going, and all three cards are active, but the performance numbers are puzzling.

The machine is set up as follows:
GPU 0: Radeon 7970
GPU 1: Radeon 7950
GPU 2: Radeon 6950

I looked up info on cgiminer.conf to get things going as optimally as possible, but I can't seem to get things going too well, because these are my numbers after a couple of hours' running:
GPU 0: 326 Kh/s
GPU 1: 324 Kh/s
GPU 2: 433 Kh/s

That's correct, the two 7xxx cards are less productive than the 6xxx card. I may not know that much about mining, but I definitely know that this is not normal.

These are the directives in my cgminer.conf:
-------------------------
"intensity" : "20",
"worksize" : "256",

"gpu-threads" : "1",
"vectors" : "1",
"lookup-gap" : "2",
"thread-concurrency" : "21712,21712,8000",

"temp-target" : "80",
"temp-overheat" : "85",
"temp-cutoff" : "90",

"scrypt" : true,
-------------------------

I must be missing something vital, does anyone have an idea what that could be?

[mikeybit]

They're different cards and each requires more input than just the TC.  ie: the Intensities need to be turned down on the 7970.

Take a look here to see what settings others have used.  https://litecoin.info/Mining_hardware_comparison

[eltopo71]

Looks like the basic problem was running three cards side by side -- I removed the 6950 and repositioned the cards so the middle PCI-E slot is empty, and I'm getting the same total performance (~1Mh/s) as I was getting with 3 cards (and saving some 150W in the process). The 7970 is generating less than the 7950 but I guess that's down to it being at 13 intensity and TC at 8192 instead of 24000 -- any more and I get nothing but HW errors from it.